I. Field
The present invention relates generally to communication, and more specifically to techniques for controlling interference in a wireless communication system.
II. Background
In a frequency hopping (FH) communication system, data is transmitted on different frequency subbands in different time intervals, which may be called “hop periods”. These subbands may be provided by orthogonal frequency division multiplexing (OFDM), other multi-carrier modulation techniques, or some other constructs. With frequency hopping, the data transmission hops from subband to subband in a pseudo-random manner. This hopping provides frequency diversity and allows the data transmission to better withstand deleterious path effects such as narrow-band interference, jamming, fading, and so on.
An orthogonal frequency division multiple access (OFDMA) system utilizes OFDM and can support multiple users. For a frequency hopping OFDMA (FH-OFDMA) system, each user may be assigned a specific FH sequence that indicates the specific subband(s) to use for data transmission in each hop period. Multiple data transmissions for multiple users may be sent simultaneously using different FH sequences that are orthogonal to one another, so that only one data transmission uses each subband in each hop period. Using orthogonal FH sequences, the multiple data transmissions do not interfere with one another while enjoying the benefits of frequency diversity.
An FH-OFDMA system typically includes many sectors, where the term “sector” can refer to a base transceiver subsystem (BTS) and/or the coverage area of the BTS, depending on the context in which the term is used. Data transmissions for users communicating with the same sector may be sent using orthogonal FH sequences to avoid “intra-sector” interference, as described above. However, data transmissions for users in different sectors are typically not orthogonalized. Each user thus observes “inter-sector” interference from users in other sectors. The detrimental effects of inter-sector interference may be reduced by defining the FH sequences for each sector to be pseudo-random or independent with respect to the FIT sequences for nearby sectors. The use of pseudo-random FH sequences randomizes inter-sector interference so that each user observes the average interference from users in other sectors. However, the randomized inter-sector interference may still significantly degrade performance for some disadvantaged users observing high levels of interference.
There is therefore a need in the art for techniques to reduce inter-sector interference in order to improve performance for disadvantaged users.